21197551 has 2 divisors, whose sum is σ = 21197552. Its totient is φ = 21197550.

The previous prime is 21197489. The next prime is 21197563. The reversal of 21197551 is 15579112.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21197551 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21197591) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10598775 + 10598776.

It is an arithmetic number, because the mean of its divisors is an integer number (10598776).

Almost surely, 2^21197551 is an apocalyptic number.

21197551 is a deficient number, since it is larger than the sum of its proper divisors (1).

21197551 is an equidigital number, since it uses as much as digits as its factorization.

21197551 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3150, while the sum is 31.

The square root of 21197551 is about 4604.0798212021. The cubic root of 21197551 is about 276.7548431061.

The spelling of 21197551 in words is "twenty-one million, one hundred ninety-seven thousand, five hundred fifty-one".